Amplifier circuit



13, 19.42! F. VAN ELDlK 2, 9 9

AMPLIFIER CIRCUIT Filed Nov. 10, 1939 3 :14 V 15 E Z INPUT v 1: E Ml you; 11-45?- 1 L 1 I2 E INVENTOR P. 5. mm FLO/K Patented Aug. 18, 1942 1 dio Corporation of America, New York, N. Y.,' a corporation of Delaware Application November 10, 1939, Serial No. 303,761 In Germany February 27, 1939 3 Claims. (Cl. 179-171) This invention relates to an amplifying circuit arrangement comprising a discharge tube which contains a cathode which is-emitting when heated, at least one control grid, an anode and an auxiliary cathode which is emitting with electron bombardment.

To obtain an increase in amplification in such a circuit arrangement, an impedance is inserted according to the invention into the circuit which is connected to the auxiliary, cathode, and part of the amplified alternating current voltage produced across the impedance in the circuit connected to the auxiliary cathode is supplied -to the control-grid circuit.

The invention is based on recognition of the fact that, due to the negative slope of the characteristic curve of the auxiliary cathode, the amplified voltage produced through the impedance cuit and the grid 3 and the impedance located in the circuit which is connected to the auxiliary cathode exhibits acomponent which is in phase with the voltage to be amplified at the control grid so that an amplificationincreasing feedback coupling can be obtained in the feed-back coupling circuit without the use of a 180 phasedisplacing transformer. a v

The invention will be more clearly understood by reference to the accompanying drawing 1 showing, by way of example," one embodiment of the circuit arrangement according thereto. It comprises a. discharge tube I which contains a cathode 2 which is emitting when heated, a control grid 3, an anode 4 and an auxiliary cathode 5 the auxiliary cathode 5 comprises a resistance l3. A point ll of, this resistance, which point is, forexample, adjustable, is connected to the control grid 3 through a coupling condenser l5.

In the circuit arrangement described the voltages to be amplified, which are supplied to the terminals 9 and ID, will bring about ,across the resistance l3 a voltage vwhich is in phase with the voltage to be amplified at the control grid 3.

Due to part of this. voltage being supplied to the control grid 3 through the coupling condenser ii, a feed-back coupling is obtained which increases the amplification.

I amplified.

It is not necessary that the impedance in the circuit connected to the auxiliary cathode 5 is an ohmic resistance. The iced-back coupling may also be obtained by using an arbitrary impedance. For obtaining a feed-back coupling which is independent of frequency, it is only I necessary that the impedance in the circuit connected to' the auxiliary cathode 5 and the impedance in the feed-back circuit, 1. e. the 1mpedance in the connection between the point I of the impedance in the auxiliary-cathode cirbetween 'the terminals 9 and ID are so chosen that the voltage supplied to the control-grid circuit is in the frequency range to be amplified in an invariable relation to the voltage to be What I claim is:

1. An amplifier circuit comprising an electron discharge tube provided with a heated cathode which emits primary electrons, a signal control grid, an anode and an unheated auxiliary cathode which is adapted upon bombardment by primary electrons to emit secondary electrons. input terminals connected respectivelyto the'control grid and to the heated cathode, output terminals connected respectively to the anode and to the heated cathode, a load impedance and a source of positive potential connected between the output terminals, an impedance connected between the auxiliary cathode and said potential source and included only in the discharge path between theztwo cathodes, and a coupling reactance connected from an intermediate point on said auxiliary cathode impedance to the control grid for obtaining an amplification-increasing feed-back of a part of the amplified alternating voltage produced across said auxiliary cathode impedance.

2. An amplifier circuit as defined in claim 1, in which an input impedance is connected between the input terminals, and the auxiliary cathode impedance, the coupling reactance and the input impedance are so chosen that the. voltage supplied to the control grid from the auxiliary cathode impedance is in the frequency range to be amplified in an invariable relation to the voltage to be amplified.

3. An amplifier circuit comprising an electron discharge tube provided with a heated cathode which emits primary electrons, a signal control grid, an anode and an unheated auxiliary cathode which is adapted upon bombardment by primary electrons to'emit secondaryelectrons, input terminals connected respectively to the control grid and to the heated cathode, output terminals connected respectively to the anode and to the heated cathode, a load resistance and a source'of positive potential connected between the output terminals, a resistance connected between the auxiliary cathode and said potentlai source, and a condenser connected on one side hating voltage produced across said auxiliary cathode resistance.

mm FREDERK VAN ELDIK. 

